A2 milk and BCM-7 peptide as emerging parameters of milk quality

Beta-casein makes up about 30% of the total protein contained in milk and can be present in cows' milk in two distinct forms (A1 or A2) or as a combination of the two. The only difference between these two variants of ?-casein (?-CN) is a single amino acid substitution. This results in a different behavior of the protein upon enzymatic cleavage, following human consumption or due to microbial action. In most of the commercially available milk containing A1 or A1/A2 ?-CN variants, the ?-casomorphin-7 peptide (BCM-7) is released upon digestion and during cheese manufacturing/ripening, while this does not happen with A2 milk. BCM-7 is a known ?-opioid receptor agonist that may influence the gastro-intestinal physiology directly and may also exert effects elsewhere in the body, such as on the cardiovascular, neurological and endocrine systems. The present article is aimed at a revision of prior review papers on the topic, with a focus on the impact of ingestion of A1 ?-CN milk and A2 ?-CN milk on any health-related outcomes and on the impact of A1 or A2 ?-CN variant on technological properties of cows' milk. When systematic reviews were considered, it was possible to conclude that A2 ?-CN exerts beneficial effects at the gastrointestinal level compared with A1 ?-CN, but that there is no evidence of A1 ?-CN having negative effects on human health. Physicochemical differences among cows' milk containing either ?-CN A2 or ?-CN A1 and their effects on technological properties are discussed.